1. Field of the Invention
The present invention relates to an asymmetric reaction catalyst and a method for preparing an optically active compound. In particular, the present invention relates to an asymmetric reaction catalyst used in nucleophilic addition and a method for preparing an optically active compound.
2. Description of the Related Art
Asymmetric nucleophilic addition reactions to the unsaturated carbon of a C═O bond or C═N bond (for example, imine (C═N) or hydrazone (C═N—N) compound) in the presence of a Lewis acid catalyst results in the formation of a new carbon-carbon bond. These reactions have been heavily examined because they can be used in the synthesis of various optically active compounds. Also, from the viewpoints of selectivity and stability, various metals and ligands are used as the above-mentioned catalyst. The inventors of the present invention have already developed an asymmetric catalyst prepared from a zirconium alkoxide and a binaphthol derivative and have reported that asymmetric Diels-Alder reactions (for example, refer to Japanese Patent Laid-open Publication 2002-356454), aldol reactions (for example, refer to Japanese Patent Laid-open Publication 2000-67833 and Yamashita et al., J. Am. Chem. Soc., 2002, Vol. 124, page 3292) and imino aldol reactions (for example, refer to Japanese Patent Laid-open Publication HII-33407) can be carried out with high yields and high stereoselectivity.
Also, it is expected that niobium has a high Lewis acidity (for example refer to C. Andrade, Tetrahedron Lett., 2001, Vol. 42, page 6473) and an example of an asymmetric Diels-Alder reaction carried out using niobium in the catalyst has been reported (for example, refer to J. Howarth and K. Gillespie, Molecules, 2000, Vol. 5, page 993).